media: cedrus: h265: Fix flag name

Bit 21 in register 0x24 (slice header info 1) actually represents
negated version of low delay flag. This can be seen in vendor Cedar
library source code. While this flag is not part of the standard, it can
be found in reference HEVC implementation.

Fix macro name and change it to flag.

Fixes: 86caab29 ("media: cedrus: Add HEVC/H.265 decoding support")
Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>